Humans and other multicellular organisms have a network of endogenous oscillators that generate repetitive diurnal changes in biochemistry, ultrastructure, physiology and behavior. Chronobiological organization has been recognized to alter during the aging process. We will test the hypothesis that these changes are a consequence of age-dependent differences in the circadian organization of membrane structure and function. Such membrane changes are presumed to be widespread in aging mammals and in aging tissues of higher plants. Circadian rhythmic leaf movements will be used as model systems for testing this hypothesis. We previously demonstrated that these turgor regulated movements are driven by a massive circadian redistribution of K ion and Cl minus ions amongst different cells in the pulvinus at the base of the leaf. The K ion and Cl ion movements are probably dependent upon H ion/K ion and Cl ion/OH ion exchange, in turn a consequence of rhythmic changes in membrane pumps and channels, with each predominant during 12 hours of the circadian cycle. Energy-dispersive x-ray analysis and secondary ion mass spectrometry of ultrathin freeze-dried sections of tissue from leaves of different ages should reveal age-dependent changes in the intracellular localization and circadian redistribution of K ion, Cl ion and also Ca2 ion, which probably participates in regulating membrane permeability to K ion. Age-dependent changes in the uptake and release of protons and other ions from the medium, will be examined using protoplasts derived from pulvini of different ages. Transport and metabolic inhibitors and temperature alteration will be used to reveal whether age-dependent changes in ion redistribution are due to active or diffusive processes. Tissue extracts from leaves of different ages will be assayed, to detect age-dependent changes in the rhythmic activity of ion-stimulated ATPases. To determine whether the clock itself, as well as the driven rhythms, change as leaves age, the effect of several chemical and physical treatments on rhythmic phase and frequency will be tested, using leaves of different ages.